Apparently I am enjoying my summer a bit too much, or just the right amount, depending on how you're measuring. I have an interesting backlog of articles to get to, just so you know I haven't forgotten about you all.
The one that's been bugging me the most is this article, titled "3 mammals that "choose" their babies sex". Now to be fair, the article does pretty quickly clarify that there's likely no "choosing" going on...but there is proof that the gender ratio at birth changes based on circumstance. I got interested in this because the last mammal on the list is human beings.
This conclusion is based on two studies. The first one found that the 400 billionaires in the US were more likely to have sons than daughters (60% sons, 40% daughters). This study got some press around the last presidential election, where it was noted that Romney had 5 sons, and Obama had 2 daughters. Apparently the higher son ratio existed irrespective of whether the wealth was fully inherited, "actively grown" or earned from scratch. This only existed for the male billionaires however...when it was the woman who had the money, she had a more even ratio of children (52% sons, 48% daughters). One of the theories behind this is that men with lots of resources have more children, whereas it appears women with lots of resources do not. This means there would be a genetic advantage to having more sons if you were at this level.
Now that's interesting to me, but I'm sort of curious what would have happened if you cross-referenced this with when the children were born in relation to the earning of the money. This whole notion is precipitated on the woman somehow knowing the resources were there first...and yet if you look at many billionaire bios, it seems that some children were born prior to any wealth (as was the case with Romney's first three sons). The study authors said that because the ratio is no different for inherited vs earned wealth, it is clearly not a quality of the males that influences the ratio (such as more testosterone = more male babies AND more financial success) , but I'm not so sure. This could be easily tested by seeing if the gender ratio shifts once money is made (could be even more interesting if the men involved had second families with different women once they made their money...would the first wife or second wife be more likely to have boys?) Also, the study authors mention they found these sex ratios by googling the billionaires....is it totally out there to think male children might be mentioned more often than female children? Especially due to last name issues?
Now, I was going to leave it at that originally, but then I was googling a bit myself, and I found this paper. It turns out someone had thought of my critiques already, and decided to go back and redo this research to try to amend for timing of earned wealth and also to get more meticulous about the counting. It turns out male children ARE more likely to be mentioned in Wikipedia pages, and that the real ratio is 52% sons/48% daughters (general population is 51%/49%). It also turns out that those with inherited wealth are more likely to have more sons than daughters (57%/43%), and those who worked for it are slightly (but not statistically significantly) more likely to have sons than daughters.
Now I don't think it's too hard to figure out why sons come up more in google searches than daughters...my guess is more sons take an active part in the family business and more daughters change their last names so they may appear to be unassociated with the father. I think this whole thing highlights how important raw data source is when trying to study something. I mean, the authors of the first paper did multiple regressions, but they didn't bother to spend much time making sure that Wikipedia was accurate???? My guess is far fewer people know about the refutation of this paper than the original.
Anyway, it's an interesting case of researchers confirming their own expectations. No one went back to check the crazy ratio of sons/daughters, because they expected a skew. It also shows how weirdly people use evolution at times...essentially the first paper argued that (for some) there was a selection effect happening before the event that should have skewed things actually occurred. Timing is important, not just outcomes. It's not that sex selection doesn't occur, but I would be hesitant to assign a specific mechanism without more data.